Dental pain is a complex sensation requiring the processing and integration of neural information at several levels of the central nervous system. Unlike other cutaneous and visceral structures, the natural stimulation of the tooth pulp or surrounding dentin produces sensations which are perceived predominately as painful. This unique sensory aspect of teeth suggests that studies designed to assess the processing of sensory information from dentin and the tooth pulp will provide useful insights into the neural mechanisms that produce pain. Neuroanatomical and electrophysiological procedures will be used to identify the somatotopic and functional representation of the dentition within the trigeminal nuclear complex. Nociresponsive trigeminal regions activated by procedures which selectively activate either A-delta or C- fibers innervating the maxillary canine will also be identified. A separate series of studies will examine the ability of morphine to produce dose-dependent, opioid-receptor mediated changes in measures of synaptic activity in response to procedures which selectively activate either A-delta or C-fiber nociceptors innervating the maxillary canine. The outcomes of these studies are consistent with the long term goals of this research program since they will advance our understanding of the neural mechanisms underlying the coding and modulation of neuronal responses to noxious orofacial stimulation.